2 Java Basic n Method(Function) New

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Java Basics


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So, what is Java?

According to Sun's definition:Java is a " simple, object-oriented,interpreted, robust, secure,architecture-neutral, portable,

high-performance, multithreaded,and dynamic language. "


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multitasking infers the mechanism to runmany processes simultaneously with userinteraction.

in contrast,multithreading is a mechanismof running various threads under single

process within its own space.


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Java Environment

EditorDraft .java file

Compiler .java file

.class File

Byte code VerifierByte code on RAM Verified Byte code

InterpreterVerified Byte codeExecuted machinecode

Class Loader .class File Byte code on RAM


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Compiling/Running Java

ProgramsTo compile your program, use command:

c:\> javac MyProgramName.javaTo run your program, use command:

c:\> java MyProgramName


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Program skeleton1 //the skeleton of a java application

2 package packagename;

3 import packagename.ClassName;

4 public class ProgramName

5 {

6 // Define program variables here.7 . . .

8 // Define program methods here.

9 . . .

10 //Define the main method here.

11 public static main(String args[])

12 {

13 // Main method body

14 }//end of the main method.

15 } //End of class HelloWorld

Java is a casesensitive language

Braces must occuron matching pairs

Coding stylesshould be followed.

Notes


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Comment StylesComments are used to clear the logic of the codeand to increase the readability if it.Comments are ignored by the compiler.Java uses three types of comments: Single-line comment( // ). Example :

//single-line comment here Multiple-line comment( /**/ ). Example :

/*

line 1 hereline 2 here

*/ Documentation comment( /***/ ). It is multiple-line

and used with javadoc utility to create applicationdocumentation.


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Playing With Strings

A string is a group of charactersWe use class String to define a string.

Example : String name;

Strings are bounded by double quotations. Example : String name = Jane;

We can concatenate two or more strings using theoperator +Strings can contain escape characters like \n ,\t , \\ , \ .


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Variables DefinitionVariables are used to represent the data that aprogram deals withAs the name might imply, the data that avariable holds can change.We have to define a variable before using itHere is an example of defining a variable:

int numberOfChar;String nameOfPerson;


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Identifiers

An identifier may contain combinations of theletters of the alphabet (both uppercase A-Z andlowercase a-z), an underscore character _, a

dollar sign $, and decimal digits 0-9.

Assignment Statement:

identifier = literal ; identifier = identifier ; identifier = expression ;


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What's a Java Literal?A constant value in a program is denoted by aliteral. Literals represent numerical (integer orfloating-point), character, boolean or string values.

Example of literals: Integer literals: 33 0 -9Floating-point literals: .3 0.3 3.14

Character literals: '(' 'R 'r '{ Boolean literals:(predefined values) true falseString literals: "language" "0.2" "r" ""


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the following statements are legal .tax = 135.86; where 135.86 is a numeric literaltax = incomeTax; where incomeTax is another identifiertax = 0.175*cost; where 0.175*cost is an expression

the following statements are illegal .135.86 = tax ; this implies the syntax literal =identifier (wrong)

tax = incomeTax statement delimiter ; missing (wrong)0.175*cost = tax; this implies expression = identifier (wrong)


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Variable Declaration:data-type identifier ;data-type identifier-list ;

int parkingTime;float balance;float costOfGas;

int weightLimit, parkingTime;float balance, costOfGas, valueOfShares;


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Variable Initialization :data-type identifier = literal ;

char parkingSymbol= 'P';int weightLimit = 10;

float balance = 1225.11f;

Constant Declaration:

final data-type identifier = literal ;

final float SALES_TAX = 0.05f;

final double PI = 3.14159;


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Casting

SYNTAXCast operation:

(data-type ) expression ;

float money = 158.05;

int looseChange = 275;money = (float) looseChange;


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Primitives Data types

Type Size in bits Valuesboolean 8 true or false

char 16 \u0000 - \uFFFF

byte 8 -128 - 127short 16 -32,768 32,767

int 32 -2,147,483,648 - +2,147,483,647

long 64-9,223,372,036,854,775,808 -+9,223,372,036,854,775,807

float 32 -3.40292347E+38 - -+3.40292347E+38

double 64 -1.79769313486231570E+308 to -

+1.79769313486231570E+308


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Arithmetic Operations

Operation Operator Java Expression

Addition + a + 8Subtraction - b - 7Multiplication * p * 10Division / c / 9Modulus % b % 6


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ArithmeticUnary Operators

+ unary plus- unary minus

Binary Multiplicative Operators * multiplication

/ division% remainder

Binary Additive Operators + addition- subtraction


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Decision making operations

Operation Operator Java Expression

Equal to == if (x == 1)

Not equal to != if (y != 5) Greater than > while (x > y)

Less than < while (x < y)

Greater than or equal >= if (X >= y)

Less than or equal


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Assignment Operators

Operator Expression Equivalent to= c = 5; c = 5

+= a += 10 ; a = a + 10;-= a -= b; a = a b;*= c *= 13; c = c * 13;

/= a /= b; a = a/b;%= b %= c ; b = b% c;


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Increment /decrement

operationOperator expression Equivalent to

++ count++;++count;

count = count + 1;

-- --count;count--;

count = count - 1;


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Logical OperatorsLogical operators allow more complex conditions&& (logical AND) Returns true if both conditions are true

|| (logical OR) Returns true if either of its conditions are true! (logical NOT, logical negation) Reverses the truth/falsity of its condition Unary operator, has one operand

Short circuit evaluation Evaluate left operand, decide whether to evaluate right

operand If left operand of &&is false , will not evaluate right

operand


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PrecedenceOperator Associativity( ) From left to right

++ -- From right to left

* / % From left to right

+ - From left to right

< >= From left to right== != From left to right

& From left to right

^ From left to right

|From left to right

&& From left to right

|| From left to right

?: From right to left

= += -= *= /= From right to left

High

Low


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Java Key words

Ja va Keyw ord s

abstract boolean break byte case

catch char class continue default

do double else extends false

final finally float for if

implements import instanceof int interface

long native new null package

private protected public return short

static super switch synchronized this

throw throws transient true try

void volatile while

Keywords that are reserved but not used by Javaconst goto

Keywords are words reserved for Java and cannot beused as identifiers or variable names


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If if/else structuresif statement looks like:if (condition){

}Conditions areevaluated to either trueor false

If/else statement lookslike:

if (condition)

{//do something.

}else

{//do something else.

}


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The switch Structure

switch statements Useful to test a variable for different valuesswitch ( value ){

case '1':actions

case '2':actions

default:actions

} break; causes exit from structure


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While Structure while repetition structure

Repeat an action while some condition remains true while loop repeated until condition becomes false

Body may be a single or compound statement If the condition is initially false then the body will never

be executed Example :

int product = 2; while ( product


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The for Structure

for "does it all" : initialization, condition, incrementGeneral formatfor ( initialization ; loopContinuationTest ; increment )

statement

If multiple statements needed, enclose in bracesControl variable only exists in body of for structureIf loopContinuationTest is initially false , bodynot executed


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public void hitungNilaiV(int n){

double nilaiV;for(int P=1000;P


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MethodsMethods

Modularize a program All variables declared inside methods are local variables

Known only in method defined

Parameters

Communicate information between methods Local variables

Benefits Divide and conquer

Manageable program development

Software reusability Existing methods are building blocks for new programs Abstraction - hide internal details (library methods)

Avoids code repetition


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Method DefinitionsMethod definition format return-value-type method-name ( parameter-list )

{ declarations and statements

} Method-name: any valid identifier Return-value-type: data type of the result (default int )

void - method returns nothing

Can return at most one value Parameter-list: comma separated list, declares

parameters.


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Methods and Parameters

SYNTAXMethod Signature:modifier(s) return-type methodName ( formal-parameter-

list );

modifier(s) usually indicates the visibility of the method,i.e., where it can be activated from. If you will notice that

the modifier defined for those methods is public ; thisimplies that the methods are visible (accessible) anywherethe class is visible. public, private dan protected


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return-type the return type specifies the data type of thevalue that is returned by the method. This can be a

primitive data type or a class . If no data is returned bythe method, then the keyword void is used for thereturn type.

methodName an identifier that defines the name of themethod.

formal-parameter-list declares the data variables thatare passed to and used by the method. If no data ispassed to the method, then the parentheses remainempty.


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return StatementWhen method call encountered Control transferred from point of invocation to

method

Returning control If nothing returned: return;

Or until reaches right brace If value returned: return expression ;

Returns the value of expression

Example user-defined method: public int square( int y )

{return y * y

}


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Calling methodsThree ways Method name and arguments

Can be used by methods of same classsquare( 2 );

Dot operator - used with references to objectsg.drawLine( x1, y1, x2, y2 );

Dot operator - used with static methods of classes

Integer.parseInt( myString );


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Coercion of argumentsForces arguments to appropriate type for method Example:

Math methods only take double Math.sqrt( 4 ) evaluates correctly

Integer promoted to double before passed to Math.sqrt

Promotion rules Specify how types can be converted without losing data If data will be lost (i.e. double to int), explicit cast must

be used If y is a double ,

square( (int) y );


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Duration of Identifiers

Duration (lifetime) of identifiers When exists in memory Automatic duration

Local variables in a method

Called automatic or local variables Exist in block they are declared When block becomes inactive, they are destroyed

Static duration Created when defined Exist until program ends Does not mean can be referenced/used anywhere

See Scope Rules


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Scope Rules (1)

Scope Where identifier can be referenced Local variable declared in block can only be

used in that blockClass scope Begins at opening brace, ends at closing brace

of class

Methods and instance variables Can be accessed by any method in class


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Scope Rules (2)

Block scope Begins at identifier's declaration, ends at terminating

brace

Local variables and parameters of methods When nested blocks, need unique identifier names

If local variable has same name as instance variable Instance variable "hidden"

Method scope For labels (used with break and continue ) Only visible in method it is used


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Method Overloading

Method overloading Methods with same name and different parameters Overloaded methods should perform similar tasks

Method to square int s and method to square double s

public int square( int x ) { return x * x; } public float square( double x ) { return x * x; }

Program calls method by signature Signature determined by method name and parameter types Overloaded methods must have different parameters

Return type cannot distinguish method


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Arrays Array Group of consecutive memory locations Same name and type Static(Remain same size)

To refer to an element, specify Array name Position number

Format : arrayname [ position number ] First element at position 0

Every array knows its own lengthc.length


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Declaring/Allocating ArraysDeclaring arrays Specify type, use new operator

Allocate number of elements Place brackets after name in declaration

Two steps:int c[]; //declarationc = new int[ 12 ]; //allocation

One step:int c[] = new int[ 12 ]; Primitive elements are initialized to zero or

false while Non-primitive references are

initialized to null


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References and Reference

ParametersPassing arguments to methods Call-by-value: pass copy of argument Call-by-reference: pass original argument

Improves performance, weakens security

In Java, you cannot choose how to passarguments Primitive data types passed call-by-value References to objects passed call-by-reference

Original object can be changed in method

Arrays in Java treated as objects Passed call-by-reference


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Passing Arrays to

Functions Passing arrays Specify array name without brackets

int myArray[ 24 ]; myFunction( myArray );

Arrays passed call-by-reference Modifies original memory locations

Header for method modifyArray might be

void modifyArray( int b[] )Passing array elements Passed by call-by-value Pass subscripted name (i.e., myArray[3] ) to method


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2 Java Basic n Method(Function) New

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